This application claims priority Japanese Patent Application No. 2000-398289, filed Dec. 27, 2000 in Japan, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an atomic beam control apparatus and method, especially an apparatus and method to control the position of an atomic beam irradiated with a light beam while passing through a multiple-pole magnetic field.
When an atomic beam is irradiated with appropriately adjusted laser light, the atoms experience a scattering force derived from the recoil which is caused in the process of spontaneous emission of light (photon) after having absorbed the laser light, or a dipole force that is produced as the spatial nonuniformity of light intensity acts upon atoms is generated.
By exerting the force caused by these effects on the atoms, it is possible to control the motion of these atoms. Lithographic technology using an atomic beam is widely known as an example of an application of this technology (hereinafter the lithographic technology is referred to as atomic lithography). Successes have been reported in forming atomic structures with a line width as fine as not more than 100 nm, which is a level exceeding the limits of conventional optical lithography on silicon substrates. Atoms such as Na (refer to V. Natsarajan et al., Phys. Rev. A53 (1996), pp. 4381-4385), Cr (refer to W. R. Anderson et al., Phys. Rev. A59 (1999), pp. 2476-2485), and Al (refer to R. W. McGowan et al., Opt. Lett. 20 (1995), pp. 2535-2537 are reported.) are reported to form such atomic structures.
2. Description of the Related Art
In the reports with the aforementioned references, attempts to produce an atomic structure directly on a substrate with a precision level less than light wavelength have been ongoing, using an atomic beam and a standing wave caused by the interference of light. In the atomic lithography that has so far been developed, however, the control of the patterning position on a substrate and the spatial positioning of an atomic beam by manipulating the atomic beam have not been attempted.
The conventional atomic lithography process can produce patterns only at the intersection (one point) of an atomic beam as the atom source and a substrate that is a pattern-forming surface. For this reason, the space for producing patterns, which the conventional atomic beam-based lithography process can draw, is limited.
FIG. 9 is a diagram for explaining the operating principle of the magneto-optical trap for atoms. The magneto-optical trap is well known in literature, such as E. L. Raab et al., Phys. Rev. Lett. 59 (1987), pp.2631-2634.
FIG. 9 shows the state where the energy level of atoms is subjected to Zeeman effect in a B-field (B=b z, where b is a constant) applied in the Z direction. In the interest of simplicity, a state where the ground state is J=0, and the excited state is J=1 is shown in the figure. In this state, "sgr"+-polarized (hereinafter referred to as positively circularly-polarized) light is applied in the +z direction, while"sgr"xe2x88x92-polarized (hereinafter referred to as negatively circularly-polarized) light is applied in the xe2x88x92z direction, with the light frequencies of both detuned slightly (by a fewxcx9cdozens of MHz) to the negative side from the resonant frequency between the ground state and the excited state of the atoms.
In the z less than 0 region, where the transition frequency toward (S=0, ms=0 S=1, ms=1) is nearer to the laser frequency than the transition frequency toward (S=0, ms=0 S=1, ms=1), the atoms absorb the positively circularly-polarized light more than the negatively circularly-polarized light, and receive a scattering force in the +z direction. In the z greater than 0 region, on the contrary, the atoms receive a scattering force in the xe2x88x92z direction. As a result, the atoms receiving a force toward z=0 at any position z are guided to the axis of z=0, and the movement of the atoms in the z direction is suppr essed by the effect of laser cooling.
It is an aspect of the present invention to provide an atomic-beam position control apparatus and method for two-dimensionally moving and stabilizing the pattern-forming position of atoms on a substrate to a desired position by creating an atomic beam which has characteristics suitable as an atomic source for atomic lithography technology and automatically controlling the spatial position of this atomic beam. Further, the present invention realizes the spatial positioning of the pattern-forming position of the atoms on the substrate and the expansion of the pattern-forming area.
According to an aspect of the present invention, there is provided a target position is set by automatically controlling the position of an atomic beam two-dimensionally using the aforementioned operating principle.
According to an aspect of the present invention, there is provided a probe light generating section for generating probe light to detect the position of the atomic beam, a light sensor for receiving the probe light, and a current control section for controlling currents flowing in multiple-pole magnetic field generating electrodes for controlling the position of the atomic beam on the basis of the output values of the light sensor in an atomic-beam control apparatus. Thus, the atomic beam control apparatus of the present invention controls the position of the atomic beam by forming a two-dimensional magneto-optical trap by irradiating the atomic beam passing through the multiple-pole magnetic field with a light beam. Further, the present invention also makes it possible to select the isotope in an atomic beam, make an atomic beam more collimated and denser, and control the spatial position of the atoms in the atomic beam.